package demo1;

import com.sun.source.tree.Tree;

import java.util.ArrayList;
import java.util.List;

public class BinaryTree {
    static class TreeNode{
        public char val;
        public TreeNode left;
        public TreeNode right;

        public TreeNode(char val) {
            this.val = val;
        }
    }

    public TreeNode root;//将来这个引用指向根节点


    public TreeNode createTree() {
        TreeNode A = new TreeNode('A');
        TreeNode B = new TreeNode('B');
        TreeNode C = new TreeNode('C');
        TreeNode D = new TreeNode('D');
        TreeNode E = new TreeNode('E');
        TreeNode F = new TreeNode('F');
        TreeNode G = new TreeNode('G');
        TreeNode H = new TreeNode('H');
        A.left = B;
        A.right = C;
        B.left = D;
        B.right = E;
        C.left = F;
        C.right = G;
        E.right = H;

        return A;
    }

    //前序遍历
    public void preOrder(TreeNode root) {
        if(root == null) {
            return;
        }
        System.out.print(root.val + " ");
        preOrder(root.left);
        preOrder(root.right);
    }


    //中序遍历
    public void inOrder(TreeNode root) {
        if(root == null) {
            return;
        }

        inOrder(root.left);
        System.out.print(root.val + " ");
        inOrder(root.right);
    }


    //后序遍历
    public void postOrder(TreeNode root) {
        if(root == null) {
            return;
        }

        postOrder(root.left);
        postOrder(root.right);
        System.out.print(root.val + " ");
    }


    //前序遍历
    public List<TreeNode> preOrder2(TreeNode root) {
        List<TreeNode> ret = new ArrayList<>();
        if(root == null) {
            return ret;
        }
        List<TreeNode> leftTree = preOrder2(root.left);
        ret.addAll(leftTree);
        ret.add(root);
        List<TreeNode> rightTree = preOrder2(root.right);
        ret.addAll(rightTree);
        return ret;
    }


    //获取第k层的个数
    public int getKLevelNodeCount(TreeNode root, int k) {
        if(root == null){
            return 0;
        }
        if(k == 1){
            return 1;
        }
        return getKLevelNodeCount(root.left, k-1)+getKLevelNodeCount(root.right, k-1);
    }

}
